In a radio system that uses orthogonal frequency division multiplexing (OFDM) modulation to perform multiple-input and multiple-output (MIMO) transmission, a desired reception characteristic can be obtained by using maximum likelihood detection (MLD) demodulation. This results from a small amount of interference from an adjacent symbol in each of sub-carriers in OFDM. In a radio system, such as code division multiple access (CDMA), where an influence of multipath interference is large, however, a wide range of window to be influenced by the multipath is assumed; thus, MLD is performed for all patterns of many adjacent symbols. Accordingly, the processing volume is increased exponentially.
To solve this problem, a method has been proposed for removing multipath interference, before performing MLD processing, by using a multipath interference canceller based on minimum mean square error (MMSE)
Non-Patent Document 1: Dirk Wubben et al, “MMSE Extension of V-BLAST based on Sorted QR Decomposition”, IEEE 2003. Non-Patent Document 2: Noriyuki Maeda et al, “QRM-MLD Combined with MMSE-Based Multipath Interference Canceller for MIMO Multiplexing in Broadband DS-CDMA”, IEEE 2004.
Since the computation volume of the multipath interference canceller alone is high, however, the computation volume for an entire apparatus is still high. Therefore, power consumption for computation processing is large, making it difficult for the apparatus to be implemented on a portable terminal which permits limited power consumption. Furthermore, a plurality of high-performance processors are provided in some cases for achieving high-speed computation, making it difficult for the apparatus to be mounted on a portable terminal with limited packaging area.